Luminescent transition metal complexes have been widely studied for their use in biological imaging, photochemical catalysis, and light-driven fuel production. Conventionally, Pt and Ru based emitters have been used, but the high cost of such emitters has led to the investigation of Cu as a lower cost, biologically relevant replacement. To that end, the most thoroughly studied Cu emitters are monomers supported by modified polypyridine and phenanthroline ligands. However, these complexes suffer from low quantum efficiencies and short luminescence lifetimes.
In an effort to address the quantum efficiency and luminescence lifetime shortcomings of the polypyridine and phenanthroline supported Cu emitters, bulky bidentate phosphines using tertiary phosphines and substituted phenanthroline ligands in concert have been investigated. These complexes inhibit exciplex quenching, which provides longer lifetimes and improved quantum efficiency. The use of bulky diphosphine ligands in simple phosphine complexes of copper halides has also been researched. However, although these complexes can be highly emissive in the solid state in low temperature solvent glasses, they display only faint, short-lived emission in solution at ambient temperatures.
Recently, amide-bridged dicopper complexes, such as [(PNP)Cu]2 (PNP−=bis(2-(diisopropylphosphino)phenyl)amide) have been researched. These dimeric copper complexes possess both long lifetimes and highly efficient emission. However, the complex ligands required to produce such dimers are difficult to manipulate, which makes changing the properties of the dimer challenging.